Modulation Scheme for Minimizing the Difference in Device-Level Current Stress in FBSM-MMC

In this article, a new modulation scheme is proposed to minimize the device-level current stress in full-bridge submodule based modular multilevel converter (FBSM-MMC), operating under extended modulation. Unlike conventional methods, the proposed approach inserts submodules as a combination of positive and negative voltages. This unique strategy alters device loading patterns, effectively redistributing the root-mean squared (RMS) current throughout the submodules. A key advantage of this approach is the elimination of complex measurements or additional control strategies common in existing methods. Furthermore, this method avoids the drawbacks associated with adapting methods designed for half-bridge submodule based MMC. The proposed scheme also offers the advantage of lower overall losses as compared to conventional methods. This article presents detailed mathematical analysis of RMS currents in both conventional and proposed approaches. Finally, the theoretical findings are validated through a laboratory-scale experimental prototype.